Crovect needs to be applied every six weeks during the 'fly' season, which varies around the country but starts sometime round about late May and ends late Sept, early Oct. We apply ours using a plant sprayer as much less is wasted, and judge the amount visually compared with the dose given by the dosing gun. The areas to concentrate on are over the rump and tail, between the back legs, over the shoulders and along the back, and a bit on top of the head. In tups, the wool around the sheath is worth a quick spray too.
Panacur is a mild wormer given by mouth, which works well especially if you have only a few sheep. If your sheep have no contact with other animals and are on ground which has not had sheep on for several years, then they will not need to be wormed frequently. If on the other hand they are crowded on 'dirty' land then you may need to worm more frequently. Older animals tend to become more resistant to worms so they also need worming less frequently. Lambs may need to be wormed from once to 3 times over the first summer, but some breeders worm them every six weeks. You can find out if your sheep need to be wormed by asking your vet to do a faecal worm count, then as you get more experienced you will learn the symptomsd of worms and know when to worm. The latest veterinary advice (from Mordun research) is only to worm when necessary, only to worm those individuals which need it, and not to move them onto fresh ground, all in an effort to reduce the development of worms which are resistant to the wormers.
Both Crovect and Panacur are expensive, so if you have only a few sheep you should find that your vet will dispense the number of doses you need, certainly for Panacur. If you are buying a whole bottle, make sure that the 'use by' date is as far ahead as possible. You must also record that you have dosed your sheep in your medecines record book.
If you are unsure of how to use either product, then do consult with your vet, rather than accidentally under or overdosing.